There is also quite a few of endemics recorded for Japan, (probably develloped due to isolation on the various islands?), but I don't really expect to see those in China: Nagurus galleranii (Arcangeli, 1927); Nagurus kunigamiensis Nunomura, 1992; Nagurus lineatus Nunomura, 1987; Nagurus miyakoensis Nunomura, 1987; Nagurus okinawaensis Nunomura, 1992; Nagurus tokunoshimaensis Nunomura, 1987;

So, the best bet is probably cristatus, nanus, sundaicus or verhoeffi. My money is on cristatus but I'll try to find out more about the others.

Originally posted by sswroom at 2010-12-30 00:14
Are there any external features which can aid for the identification?

The features used in IDing can be quite diverse and sometimes minute details of genitalia or other parts are needed. In 90% of the cases however larger morphological features will do the trick and for someone who is experienced with the local range of species one dorsal shot will often be enough. For someone like me, who is just beginning to find out about Asian species that won't work, and I would need to see as many of the "usual" features as possible to be able to get anywhere with the little literature I might be able to dig up.

Anyway, more or less in order of importance/usefulness:

Full dorsal shot. This will make a very rough first selection possible based on general habitus. In general there are three basic types of habitus but intermediates also exist:

"Clinger" - broad and flat. Animal can pull itself to the substrate and the flattened epimera will make it hard to get a grip under it. Typical habitus such as Porcellio scaber or the Nagurus above.

"Runner" - less flattened and higher on the legs. First line of defense is to dart off. Typical habitus such as the "Burmoniscus" (Philosciidae) above.

"Roller" - higher rounded habitus with epimera falling almost straight down. First line of defense is to roll into a ball.

Many species will be clearly or mildly indented on the separation between thorax ("pereon", sometimes "pereion") and abdomen ("pleon"), where the pleon is (much) narrower than the pereon. This is most typical for "runners". More often than not these will also be relatively smooth bodied. The degree of narrowness of the pleon is often a very important first indicator in ID (cf. this comparison).

Also important in ID is the smoothness or roughness of the dorsal surface, and or the presence of scales or even "hairs"

Another feature often used from the first dorsal shot (or a tad lateral) is the exact shape of the epimera of pereon and pleon (the little "wings" extending to the sides of the dorsal plates). For example compare the hind corner of the first pereonite (tergal plate) of your Nagurus (almost right-angled slightly forward) with that of the omnipresent Porcellio scaber (sinuoid and sharply backward pointing). On the pleon the epimera can be extending outward in various degrees (again: Porcellio) or almost snugly wrapped around the body (as in the runner above).

A very important ID-ing feature, almost without fail, is the exact shape of the uropods (the two tail appendages) and the telson (central terminating dorsal plate). Always try to get some high res shots of the tail! Very typical for the genuine "rollers" is that these appendages have evolved into more plate like structures that do not extend outside the body (cf. images 1-4 above)

The whole of the head structure is equally important. One or more perspectives can really clear things up - the staring point being frontal/lateral/above (about 45 degrees on all three axis). Features to look for are these: Smoothness/tubercles; Shape and size of the eyes (if any); Shape of the frontal edge of the head: smoothly rounded, pointed forward or even with clearly extended central and lateral lobes (cf. the cute notched central lobe on your Nagurus). For conglobating species such as the Armadillidae in 1-4 above the shape of the front of the head is an important help, either with or without central triangle (scutellum) and with various structures/ridges to guide the antennae when rolled into a ball.

One other "head" feature that is often used as one of the first steps in dichotomous keys is the exact shape of the antenna and more specifically that of the last segments - the flagellum. Various basic shapes are recognized that divide the main groups of woodlice. If the observer is able to count the segments in the flagellum (or recognize that these are indistinguishable) than that is a good antenna shot. Basic variants: 2 or 3 segments; 10 or more; cone shaped with segments fused;

The most important and relatively easily inspected ventral feature is the number of pseudo tracheal organs or "lungs" if you will on the underside of the pleon (abdomen). On life animals these are visible as clear white patches on the rudimentary pseudo legs of the abdomen. Some species will have none (internal), others only on the first 2 or 3 segments and some on all five. The Nagurus above should have 5 pairs. This is of particular importance to make a quick first step in identifying the huge group of clingers and separates these in families such as Porcellionidae, Agnaridae and Trachelipodidae. Hence often found early on in keys and always a good shot to take. For those bigger species it is quite easy to pick one up between thumb and index and take a few shots of the "private" parts. The white patches will be clear even on images with motion blur, provided that the legs are not covering the pleon (hence a few shots to make sure).

Next up is the nitty gritty stuff, mostly ventral. On most species hairs, bristles, spines etc on the legs are described as IDing features. Mostly those of the 7th legs of males, but sometimes also the first legs or even for females. And of course the "genitalia", which is not really that, but rather the pleopoda (pleon-legs, rudimentaire legs of the abdomen) of the first two pleon segments that have developed into copulatory helper organs (cf. the extended white plates on the male in this image). Sometimes the important shapes can be estimated on a life animal (very high res images), but usually it will take dissecting and microscopic examination.

I think I've just about reached my quotum for uploads so there is little point in sorting out images to support all that. Well, too bad, tough luck. Maybe some other time.
Cheers, Arp

P.S. Oh well, I'll work in some links. This collage shows a number of good angles for ID shots. This example shows a typical set of IDing features from (old) literature.